The present invention relates to a pressure-sensitive adhesive composition which is a non-pressure-sensitive adhesive or a low pressure-sensitive adhesive (tack free) at room temperature, pressure-sensitive adhesive sheets made from the foregoing composition in the state of a sheet form, a tape form, etc., and a sealing material, a reinforcing sheet, and a printable pressure-sensitive adhesive sheet using them.
A pressure-sensitive adhesive usually has a storage elastic modulus [Gxe2x80x2] at room temperature of about 1xc3x97106 dyne/cm2 or lower as described in D. Satas, Adhesive Age, 31(9), 28(1988). When the storage elastic modulus of a pressure-sensitive adhesive at room temperature is increased, the pressure-sensitive adhesive becomes too hard and becomes non-adhesive. This is because a micro-contact of the pressure-sensitive adhesive and the adherend is not sufficiently carried out in the adhesive step as in a wrapping film for foods, namely, the wrapping films are visually (optically) adhered to each other, but the adhesion is not exhibited.
However, because a conventional pressure-sensitive adhesive has a softness in a sticky state having a tackiness, the pressure-sensitive adhesive adheres quickly. But, it is not easy to peel the pressure-sensitive adhesive adhered by lightly contacting, and thus, the correction of the position is difficult. Also, in processing such as cutting, punching, etc., of a pressure-sensitive adhesive sheet, there is a problem that the processing edge is stained with the pressure-sensitive adhesive.
If the storage elastic modulus of the pressure-sensitive adhesive is increased to solve these problems, the adhesive property is lowered along with the tackiness as described above, and thus the adhesion to an adherend is difficult without an adhesive assisting means such as heat treatment.
As described above, a pressure-sensitive adhesive which has a high elasticity and non-pressure-sensitive adhesion or low pressure-sensitive adhesion (tack free) capable of preventing lowering of adhesive workability, etc., and also is excellent in the adhesion has not yet been found.
Under such circumstances, an object of the present invention is to provide a pressure-sensitive adhesive composition which shows an excellent adhesion while exhibiting a high elasticity and tack free at about room temperature, and hence can cope with the adhesive workability and the adhesion, and a pressure-sensitive adhesive sheet having the composition.
Also, other object of the present invention is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which are excellent in the durability, the heat resistance, etc., and further to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which are also excellent in the self-adhesion in addition to the durability such as the heat resistance, weather resistance, etc.
Other object of the present invention is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which show a good adhesion to various adherends and are excellent in the creep characteristics and the long-term durability and also is to provide the above-described pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets using the composition, which satisfy the creep resistance and the adhesion in a high temperature range and are excellent in the shock resistance in a low-temperature range.
Furthermore, still other object of the present invention is to provide the above-described pressure-sensitive adhesive sheets using a release liner not subjected to a silicone release coating and thus suitable for computer instruments which are liable to cause problems by the existence of a silicone, and in particular to provide the above-described pressure-sensitive adhesive sheets which are excellent in the releasing property of the above-described liner and show a good adhesive strength.
Also, other object of the present invention is to provide pressure-sensitive adhesive sheets which can be wound in a roll form without using a release liner and are suitable for the uses such as computer instruments as pressure-sensitive adhesive sheets containing substantially no silicone compound.
The present inventors have discovered that by selecting a specific polymer for constituting a pressure-sensitive adhesive and crosslinking the polymer, a pressure-sensitive adhesive composition having specific values of the storage elastic modulus and the adhesive strength at room temperature can be obtained and the pressure-sensitive adhesive composition shows a good adhesion while having a high elasticity and being tack free, and also have discovered that a pressure-sensitive adhesive composition excellent in the self-adhesion in addition to the durability such as heat resistance and weather resistance can be obtained by specifying the solvent insoluble component of the polymer.
That is, the present invention provides a pressure-sensitive composition wherein the storage elastic modulus [Gxe2x80x2] at room temperature is at least 2xc3x97106 dyne/cm2 and the adhesive strength at room temperature is at least 1 kg/20 mm width, the pressure-sensitive composition comprising a polymer having a polycarbonate structure having a repeating unit represented by the following formula 
wherein R represents a straight chain or branched hydrocarbon group having from 2 to 20 carbon atoms, as the polymer for constituting the pressure-sensitive adhesive composition, and particularly, a pressure-sensitive adhesive composition comprising a polyester having a weight average molecular weight of at least 10,000 synthesized from diol components indispensably containing polycarbonate diol and dicarboxylic acid components indispensably containing a dicarboxylic acid having an aliphatic hydrocarbon group having from 2 to 20 carbon atoms or an alicyclic hydrocarbon group as the molecular structure. Also, according to the present invention, there is further provided a pressure-sensitive adhesive composition having the above-described construction, wherein the solvent insoluble component is from 1 to 30% by weight and the self-adhesive strength is at least 2.0 kg/20 mm width.
Also, the present inventors have discovered that by combining the polymer having the polycarbonate structure described above and a specific acrylic polymer, a pressure-sensitive adhesive composition showing good adhesion characteristics to various adherends and being excellent in the creep characteristics and the long-term durability can be obtained. That is, according to other aspect of the present invention, there is provided a pressure-sensitive adhesive composition comprising, along with the polymer having the polycarbonate structure, an acrylic polymer having a glass transition temperature of not higher than xe2x88x9210xc2x0 C. in an amount of from 10 to 90% by weight of the sum total of the above-described polymer and the acrylic polymer.
Furthermore, the present inventors have discovered that by combining the polymer having the polycarbonate structure described above and a specific resin, a pressure-sensitive adhesive composition satisfying the creep resistance and the adhesion in a high-temperature range and being excellent in the shock resistance at a low temperature can be obtained. That is, according to still other aspect of the present invention, there is provided a pressure-sensitive adhesive composition comprising, along with the polymer having the polycarbonate structure, a resin having a softening point of at least 80xc2x0 C. in an amount of from 10 to 50% by weight of the sum total of the above-described polymer and the resin.
Moreover, the present invention can further provide pressure-sensitive adhesive sheets having the above-described pressure-sensitive adhesive compositions of various constitutions formed into a sheet form, a tape form, etc., that is, pressure-sensitive adhesive sheets having a layer composed of each of the above-described pressure-sensitive adhesive compositions having the various constitutions. In such pressure-sensitive adhesive sheets, a release liner is generally stuck. to the surface of the pressure-sensitive adhesive layer thereof. As the release liner, the present inventors have discovered that a release liner made up of a polyethylene film, a polypropylene film, etc., which is not subjected to a silicone release coating, can be used, that is, a pressure-sensitive adhesive sheet exhibiting excellent releasing property of the release liner and having good adhesive strength can be obtained because of the characteristics of the pressure-sensitive adhesive composition. Accordingly, it has been discovered that pressure-sensitive adhesive sheets suitable for computer instruments, etc., which are liable to cause problems by the presence of a silicone, can be provided.
That is, according to other aspect of the present invention, there are provided pressure-sensitive adhesive sheets each having the layer made up of each of the above-described pressure-sensitive adhesive compositions of various constitutions and having stuck to the surface of the pressure-sensitive adhesive layer a release liner which is not subjected to a silicone release coating and, in particular, there are provided the pressure-sensitive adhesive sheets wherein the above-described release liner, which is not subjected to a silicone release coating, is a polyolefinic film composed of polyethylene, polypropylene, an ethylene-propylene copolymer or a mixture thereof, or a film the surface of which is processed with the polyolefin as described above, and also the releasing strength of the release liner is 200 g/50 mm width or lower.
Also, the present inventors have discovered that in the case of forming each of the above-described pressure-sensitive adhesive compositions of various constitutions on one surface of a base material, when at least the back side of the base material is constituted with a polyolefin such as polyethylene, polypropylene, etc., a pressure-sensitive adhesive sheet, which has a good releasing property between the layer made up of the pressure-sensitive composition and the back surface of the base material and thus can be wound in a roll form without inserting a release liner, can be obtained. That is, because according to the pressure-sensitive adhesive sheets, they do not have release liners and it is unnecessary to apply a silicone release coating to the back surface of each base material of them, the pressure-sensitive adhesive sheets of the present invention can be used for computer instruments, etc., which cause a problem by the presence of silicone, as pressure-sensitive adhesive sheets substantially containing no silicone compound.
In the pressure-sensitive adhesive composition of the present invention, the storage elastic modulus [Gxe2x80x2] at room temperature is 2xc3x97106 dyne/cm2 or higher, preferably 3xc3x97106 dyne/cm2 or higher, particularly preferably 5xc3x97106 or higher, and usually 5xc3x97107 dyne/cm2 or lower, and the pressure-sensitive adhesive composition does not show a high tackiness as a pressure-sensitive adhesive and scarcely adhere in a short time of about a few seconds. Accordingly, if it is a short time after adhesion, the pressure-sensitive adhesive composition can be peeled once and then adhered again, and the stuck position can be corrected without injuring an adherend. Also, in cutting the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive does not stick to the cutting edge and does not stain the edge, because the pressure-sensitive adhesive does not adhere in a short time.
Also, although the pressure-sensitive adhesive composition of the present invention has a high elasticity and is tack free as described above, the pressure-sensitive adhesive composition has an adhesive strength at room temperature of at least 1 kg/20 mm width, preferably at least 1.5 kg/20 mm width, and usually 10 kg/20 mm width or lower and is provided with the unique and useful characteristics of showing a high adhesive strength without need of complicated step such as a heat treatment. An excellent effect of satisfying both the adhesive workability and the adhesion, which is difficult in conventional pressure-sensitive adhesive compositions, can be obtained by the characteristics.
In such a pressure-sensitive adhesive composition, it is preferred that the storage elastic modulus [Gxe2x80x2] at xe2x88x9230xc2x0 C. is 3xc3x97107 dyne/cm2 or lower, preferably 2xc3x97107 dyne/cm2 or lower, and usually 5xc3x97106 dyne/cm2 or higher, and in this case, the effect that the pressure-sensitive adhesive composition is excellent in the shock resistance at a low temperature can be obtained. Also, it is preferred that the storage elastic modulus [Gxe2x80x2] at 80xc2x0 C. is 1xc3x97106 dyne/cm2 or higher, preferably 3xc3x97106 dyne/cm2 or higher, and usually 5xc3x97107 dyne/cm2 or lower, and in this case, the pressure-sensitive adhesive composition shows a high cohesive force at a temperature as high as 80xc2x0 C. and excellent characteristics are obtained together with the adhesive strength and the holding power.
The pressure-sensitive adhesive composition of the present invention has no particular restriction on the composition, as long as the composition has the above-described storage elastic modulus [Gxe2x80x2] and the above-described adhesive strength, but, preferably used is a composition which is obtained by adding a crosslinking agent such as a polycyanate compound, etc., to a polymer for constituting the pressure-sensitive adhesive and effecting a crosslinking treatment and has the storage elastic modulus [Gxe2x80x2] and the adhesive strength specified above as a result of the selection of the polymer, the extent of the crosslinking treatment and the like. With respect to the polymer for constituting the pressure-sensitive adhesive, a polymer having the repeating unit represented by the following formula is preferred as the polymer having a polycarbonate structure; 
wherein R represents a straight chain or branched hydrocarbon group having from 2 to 20 carbon atoms.
The polymer includes a polyester synthesized from a polycarbonate diol (or the derivative thereof) and a dicarboxylic acid (or the derivative thereof), the polyester synthesized from a polycarbonate dicarboxylic acid and a diol, a polyurethane synthesized from a polycarbonate diol and a diisocyanate, etc., and in these polymers, the polyester synthesized from a polycarbonate diol and a dicarboxylic acid is preferred.
The polyester of this kind has a weight average molecular weight of at least 10,000, preferably at least 30,000, and particularly preferably at least 50,000 (usually not more than 300,000) synthesized from diol components indispensably containing a polycarbonate diol and dicarboxylic acid components indispensably containing a dicarboxylic acid having an aliphatic hydrocarbon having from 2 to 20 carbon atoms or an alicyclic hydrocarbon as the molecular structure.
The polycarbonate diol used in this case is a diol having the repeating unit represented by the following formula 
wherein R represents a straight chain or branched hydrocarbon group having from 2 to 20 carbon atom, and the number average molecular weight of the diol is at least 400, preferably at least 900 (usually not more than 10,000).
Such a polycarbonate diol includes polyhexamethylenecarbonate diol, poly(3-methylpentenecarbonate) diol, polypropylenecarbonate diol, etc., a mixture thereof, and a copolymer thereof. As commercially available products of the polycarbonate diol, there are xe2x80x9cPLACCEL CD205PLxe2x80x9d, xe2x80x9cPLACCEL CD208PLxe2x80x9d, xe2x80x9cPLACCEL CD210PLxe2x80x9d, xe2x80x9cPLACCEL CD220PLxe2x80x9d, xe2x80x9cPLACCEL CD205xe2x80x9d, xe2x80x9cPLACCEL CD208xe2x80x9d, xe2x80x9cPLACCEL CD210xe2x80x9d, xe2x80x9cPLACCEL CD220xe2x80x9d, xe2x80x9cPLACCEL CD205HLxe2x80x9d, xe2x80x9cPLACCEL CD208HLxe2x80x9d, xe2x80x9cPLACCEL CD210HLxe2x80x9d, xe2x80x9cPLACCEL CD220HLxe2x80x9d, etc., trade names, made by DAICEL CHEMICAL INDUSTRIES, LTD.
As the diol components, in addition to the above-described polycarbonate diol, if necessary, other components such as straight chain diol components and branched diol components (e.g., ethylene glycol, propylene glycol, butane diol, hexane diol, octane diol, decane diol, and octadecane diol) may be used in combination. It is preferred that the used amount of these other diol(s) is not more than 50% by weight, and preferably not more than 30% by weight to the total amount of the diol components. Also, a small amount of polyol component(s) of a three functional or higher may be added to increase the molecular weight of the polymer.
Also, the dicarboxylic acid component has an aliphatic hydrocarbon group having from 2 to 20 carbon atoms or an alicyclic hydrocarbon group and the aforesaid hydrocarbon group may be a straight chain one or a branched one. Specifically, there are succinic acid, methylsuccinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecane diacid, 1,14-tetradecane diacid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, the acid anhydrides and the lower alkyl esters of these acids, etc.
As the dicarboxylic acid, it is preferred that the dicarboxylic acid having the aliphatic hydrocarbon group having from 2 to 20 carbon atoms or the alicyclic hydrocarbon group as the molecular structure is used singly but as the case may be a dicarboxylic acid having an aromatic hydrocarbon group as the molecular structure may be used together with the aforesaid dicarboxylic acid. It is better that the used amount of the dicarboxylic acid having the aromatic hydrocarbon group as the molecular structure is 50% by weight or lower, and particularly preferably an amount as small as 30% by weight or lower. Also, for the purpose of increasing the molecular weight of the polyester to be synthesized, a small amount of a tri-functional or higher functional carboxylic acid component can be added thereto.
The polyester is obtained by subjecting the diol component and the dicarboxylic acid component described above to an esterification reaction in the absence or presence of an appropriate catalyst according to an ordinary method. In this case, it is preferred that the diol component and the diarboxylic acid component are subjected to an equimolar reaction, but, the reaction may be carried out using either of them in an excessive amount in order to accelerate the esterification reaction. It is desirable that the polyester thus obtained has the above-described molecular weight. This is because if the molecular weight thereof is too low, the highly crosslinked pressure-sensitive adhesive has a high crosslinking density and thus has a very hard property, and contrary, the attempt of lowering the crosslinking density is undesirable in the heat resistance, etc., owing to the low molecular weight of the uncrosslinked components.
In the present invention, the pressure-sensitive adhesive composition, wherein the storage elastic modulus [Gxe2x80x2] at room temperature and the adhesive strength become the above-described ranges, is formed by usually subjecting such a polymer having the polycarbonate structure, such as the polyester, to a crosslinking treatment by a proper means. In this case, the crosslinking means may be arbitrary, but a general method comprises using a poly-functional compound such as a polyisocyanate compound, an epoxy compound, an aziridine compound, a metal chelate compound, and a metal alkoxide compound as a crosslinking agent and crosslinking the polymer by reacting the polymer (the hydroxy group and the carboxyl group contained therein) and the poly-functional compound. As the poly-functional compound, a polyisocyanate compound is particularly preferred.
The polyisocyanate compound includes lower aliphatic polyisocyanates such as ethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, etc.; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate, etc.; aromatic polyisocyanate such as 2,4-tolylene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, xylylene diisocyanate, etc.
As other polyisocyanate compound, the tolylene diisocyanate addition product of trimethylolpropane (Coronate L, trade name, made by Nippon Polyurethane Industry Co., Ltd.), the hexamethylene diisocyanate addition product of trimethylolpropane (Coronate HL, trade name, made by Nippon Polyurethane Industry Co., Ltd.), etc., are also used.
These polyfunctional compounds are used singly or as a mixture of two or more. The used amount thereof is properly selected according to the balance with the polymer to be crosslinked and the use application of the pressure-sensitive adhesive composition but in general, it is better to carry out the crosslinking treatment by compounding 0.5 part by weight or more, and preferably from about 1 to 5 parts by weight of the polyfunctional compound(s) per 100 parts by weight of the polymer having the polycarbonate structure. A pressure-sensitive adhesive composition in which the content of the solvent-insoluble component of the polymer is from 10 to 90% by weight, preferably from 15 to 80% by weight, and more preferably from 20 to 70% by weight can be obtained by the crosslinking treatment. If the content of the solvent-insoluble component of the polymer is too small, the insufficient cohesive force of the pressure-sensitive adhesive is exhibited and the sufficient modulus of elasticity, heat resistance, and durability can not be obtained.
As other crosslinking means, there is a method of compounding a polyfunctional monomer as a crosslinking agent with the polymer and crosslinking the polymer by electron rays, etc. The polyfunctional monomer includes ethylene glycol (meth)acrylate, pentaerithritol tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc. It is better that the used amount of the polyfunctional monomer is from 1 to 5 parts by weight, and preferably from 2 to 4 parts by weight per 100 parts of the above-described polymer such that the solvent-insoluble component of the polymer after crosslinking by electron rays, etc., is the value falling within the range described above.
The pressure-sensitive adhesive composition of the present invention is formed by using the above-described polymer having the polycarbonate structure as the base polymer and crosslinking the polymer usually by the means described above and the composition may be compounded with a conventionally known tackifier and also can arbitrarily contain various additives such as an inorganic or organic filler, a metal powder, a powder of a pigment, etc., a granular material, a foil-form material, an antioxidant, a plasticizer, etc.
The pressure-sensitive adhesive composition of the present invention shows a high adhesive strength while having a high modulus of elasticity and being tack free at room temperature, and further when the solvent-insoluble component is adjusted in the range of from 1 to 30% by weight, and preferably from 2 to 15% by weight by the crosslinking treatment of the polymer, the pressure-sensitive adhesive composition shows an excellent self-adhesion in addition to the durability such as the heat resistance, or the weather resistance. That is, the present invention can provide a pressure-sensitive adhesive composition having a self-adhesive strength of 2.0 kg/20 mm width or higher, and preferably from 2.5 to 10 kg/20 mm width. In this case, if the solvent-insoluble component of the polymer described above is less than 1% by weight, the pressure-sensitive adhesive composition is inferior in the durability such as the heat resistance, the weather resistance, etc., and if the solvent-insoluble component is more than 30% by weight, the high self-adhesive strength as described above is hard to be obtained.
In addition, hitherto, pressure-sensitive adhesives prepared by compounding a tackifier, a softening agent, etc., with a natural rubber, a synthetic rubber, etc., are known as a pressure-sensitive adhesive having a self-adhesion for bundling fresh vegetables or arranged flowers as disclosed in JP-A-54-96539 and JP-A-56-26968 (the term xe2x80x9cJP-Axe2x80x9d as used herein meas an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, because these pressure-sensitive adhesives are inferior in the weather resistance and the heat resistance, they have never been used for uses being used outdoors and used of requiring a reliability over a long period of time as industrial materials. Also, because these pressure-sensitive adhesives have a tackiness (pressure-sensitive adhesive property), there is a problem that the pressure-sensitive adhesive attaches to the hand and finger, articles, etc., before and after bounding. On the other hand, the pressure-sensitive adhesive composition of the present invention does not cause such a problem.
Furthermore, removing is difficult when removing after self-adhesion is required, and cutting of the pressure-sensitive adhesive tape is needed to release the bundling. In the cutting, there is a possibility of damaging the bundled article.
In the pressure-sensitive composition of the present invention, the polymer having the specific polycarbonate structure is contained as the main component and by crosslinking the polymer to a specific level, the pressure-sensitive adhesive composition does not substantially show a tackiness (i.e., show non-tackiness or slight tackiness at room temperature) but has an excellent self-adhesion and can be removed.
That is, the present invention provides a pressure-sensitive adhesive composition comprising, as the main component, a polymer having a polycarbonate structure having a repeating unit represented by the following formula 
wherein R represents a straight chain or branched hydrocarbon group having from 2 to 20 carbon atoms, wherein the self-adhesive strength is at least 100 g/20 mm width and the adhesive strength is not higher than 2,000 g/20 mm width, and in particular, the above-described pressure-sensitive adhesive composition in which the aforesaid polymer is crosslinked and the solvent-insoluble component is from 60 to 95% by weight.
Furthermore, the present invention provides a pressure-sensitive adhesive sheet comprising a base material having on one surface or both surfaces thereof the layer made up of the above-described pressure-sensitive adhesive composition.
In the present invention, a pressure-sensitive adhesive composition which does not substantially show a tackiness (i.e., show non-tackiness or slight tackiness at room temperature), but has a good self-adhesion and is excellent in the removability is obtained by crosslinking such a polymer having the polycarbonate structure, such as a polyester, to a specific level. In this case, the extent of crosslinking is preferably such that the solvent-insoluble component is in the range of from 60 to 95% by weight, and more preferably from 65 to 90% by weight. If the solvent-insoluble component is less than 60% by weight, a sufficient removability is not obtained and if the solvent-insoluble component is more than 95% by weight, the self-adhesive strength is lowered. Thus, both cases are undesirable.
In the crosslinking method, the crosslinking agent is the same as described above and these crosslinking agents can be used singly or as a mixture of two or more. The used amount thereof is properly selected according to the balance with the polymer to be crosslinked. In general, it is better that the ratio of the above-described crosslinking agent becomes from about 2 to 10 parts by weight to 100 parts by weight of the polymer. The use of the crosslinking agent in such a ratio enables a pressure-sensitive adhesive composition having a solvent-insoluble component falling within the above-described range.
As other crosslinking agent, a method of adding the polyfunctional monomer as described above to the polymer as a substantial crosslinking agent and crosslinking the polymer by electron beam, etc., may be employed. The used amount of the polyfunctional monomer is properly selected according to the balance with the polymer to be crosslinked and further the use application of the pressure-sensitive adhesive composition. In general, it is better that the ratio of the polyfunctional monomer is at least 3 part by weight (usually up to about 10 parts by weight) to 100 parts by weight of the polymer, and by using the polyfunctional monomer in such a proportion, the pressure-sensitive adhesive composition having a solvent-insoluble component falling within the above-described range can be obtained.
The pressure-sensitive adhesive composition of the present invention is prepared by subjecting the above-described polymer to the crosslinking treatment as described above and has a self-adhesive strength and a removability such that the self-adhesive strength is 100 g/20 mm width or higher, preferably 150 g/20 mm width or higher, and more preferably 200 g/20 mm width or higher (usually up to 1,500 g/20 mm width) and the adhesive strength is 2,000 g/20 mm width or lower, preferably 1,800 g/20 mm width or lower, and more preferably 1,500 g/20 mm width or lower (usually up to 100 g/20 mm width).
If the self-adhesive strength is less than 100 g/20 mm width, the reliability of the unity or adhere of articles is inferior and if the adhesive strength is higher than 2000 g/20 mm width, the removing is difficult.
The term xe2x80x9cself-adhesive strengthxe2x80x9d in the specification indicates the releasing strength at the initial stage after the pressure-sensitive adhesive surfaces are stuck to each other, and on the other hand, the term xe2x80x9cadhesive strengthxe2x80x9d indicates the above-described releasing strength (self-adhesive strength) after allowing to stand for one day as in the working examples described later.
Also, in the present invention, by, along with the polymer having the polycarbonate structure, using an acrylic polymer having a glass transition temperature of xe2x88x9210xc2x0 C. or lower in a ratio of from 10 to 90% by weight, and preferably from 15 to 85% by weight based on the sum total of the acrylic polymer and the above-described polymer, a pressure-sensitive adhesive composition showing. good adhesive property to various adherends in addition to the above-described characteristics and being excellent in the creep characteristics and the long-term durability can be obtained.
Hitherto, an acrylic pressure-sensitive adhesive not containing a tackifier is poor in the adhesive property to plastics, while an acrylic or natural rubber series pressure-sensitive adhesive containing a tackifier has relatively good adhesive property to plastics, but has a problem in the creep characteristics and the long-term durability. On the other hand, in the pressure-sensitive adhesive composition of the present invention, such problems are avoided, and a pressure-sensitive adhesive excellent in the adhesive property to various adherends, in particular, plastics such as polycarbonate, acrylic resins, etc., and also excellent in the creep characteristics and the long-term durability can be provided.
The acrylic polymer to be used herein is a polymer made from monomers containing from 50 to 100% by weight of a (meth)acrylate having an alkyl group having from 4 to 14 carbon atoms, and the acrylic polymer having a glass transition temperature of xe2x88x9210xc2x0 C. or lower, and particularly xe2x88x9215xc2x0 C. or lower (usually up to about xe2x88x9290xc2x0 C.) is preferably used. If the glass transition point is higher than xe2x88x9210xc2x0 C., the pressure-sensitive adhesive composition is undesirably inferior in the initial adhesive strength.
The (meth)acrylate having an alkyl group having from 4 to 14 carbon atoms includes the alkyl esters of (meth)acrylic acid having an alkyl group such as butyl, isobutyl, isoamyl, hexyl, heptyl, 2-ethylhexyl, iso-octyl, iso-nonyl, lauryl, or iso-myristyl.
In the case of using such an acrylic polymer in combination, it is general to separately synthesizing the acrylic polymer and the polymer having the polycarbonate structure, and then mixing both the polymers at a solution state or bulky state to prepare a pressure-sensitive adhesive composition. However, as the case may be, the pressure-sensitive adhesive composition may be prepared by a method of effecting polymerization for the preparation of one polymer in another polymer or a method of simultaneously effecting polymerization for both polymers.
In these preparation methods, the used amount of the above-described acrylic polymer is such that the proportion of the acrylic polymer based on the sum total of the acrylic polymer and the polymer having the polycarbonate structure falls within the range described above. If the content of the acrylic polymer is less than 10% by weight, the initial adhesive property is lowered. On the other hand, if the content is more than 90% by weight, the adhesive property to plastics is lowered. Also, one or both of the aforesaid acrylic polymer and the polymer having the polycarbonate structure are subjected to the crosslinking treatment by the method described above and in this case, it is better that the solvent-insoluble component in the whole polymers falls within the range of from 10 to 90% by weight, preferably from 15 to 85% by weight, and more preferably from 20 to 80% by weight. If the content of the solvent-insoluble components is low, the creep characteristics and the long-term durability are inferior, while if the content is too high, the initial adhesive property is inferior. Thus, both cases are undesirable.
Furthermore, in the present invention, by using a resin having a softening of at least 80xc2x0 C., together with the polymer having the polycarbonate structure, in a ratio of from 10 to 50% by weight, preferably from 13 to 45% by weight, and more preferably from 15 to 35% by weight of the sum total of the resin and the polymer, a pressure-sensitive adhesive composition satisfying the creep resistance and the adhesive property in a high-temperature range in addition to the above-described characteristics and also being excellent in the shock resistance at a low temperature can be obtained.
Hitherto, a pressure-sensitive adhesive composition containing added therein a heat-melting resin is known as described in JP-B-56-13040 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined published Japanese patent applicationxe2x80x9d). The pressure-sensitive adhesive composition has advantages that the treatment work is simple and a heat resistance is not required for an adherend as compared with a heat-curing type requiring a heat treatment of 100xc2x0 C. or higher but on the other hand, there is a problem in obtaining the creep resistance and the adhesive property in a high-temperature range.
Also, in JP-B-2-50146, a product obtained by adding a heat-melting resin in an acrylic graft polymer having a polymer of a high glass transition temperature at the side chain thereof is disclosed. The product satisfies the creep resistance and the adhesive property at a high-temperature range, but has a problem that it has poor shock resistance at a low temperature.
On the other hand, the pressure-sensitive adhesive composition of the present invention described above does not have such a problem, and a heat pressure-sensitive adhesive composition satisfying the creep resistance and the adhesive property at a high-temperature range and being excellent in the shock resistance at a low temperature can be provided.
The resin used in this case of the present invention has a softening point of 80xc2x0 C. or higher, preferably 90xc2x0 C. or higher, and more preferably 100xc2x0 C. or higher and usually not higher than 150xc2x0 C. The softening point of lower than 80xc2x0 C. is undesirable, since the creep resistance and the adhesive strength at a high temperature are lowered.
As the kind of the resin, there are a terpene series resin, a rosin series resin, an alkylphenol series resin, a terpene phenol series resin, a rosin phenol series resin, a coumarone-indene series resin, an aromatic petroleum series resin, an aliphatic petroleum series resin, etc.
If the ratio of the resin of this kind is less than 10% by weight of the sum total of the resin and the polymer having the polycarbonate structure, the shock resistance at a low temperature is inferior.
Also, it is better that the solvent-insoluble component of the polymer containing the resin after the crosslinking treatment is in the range of from 10 to 90% by weight, preferably from 15 to 85% by weight, and more preferably from 20 to 80% by weight. If the content of the solvent-insoluble component is too low, the durability is inferior and if the content is too high, the adhesive property is inferior. Thus, both cases are not desirable.
The pressure-sensitive adhesive sheets of the present invention are a sheet-form or tape-form formed by the pressure-sensitive adhesive compositions of the various constitutions described above. That is, the pressure-sensitive adhesive sheets have at least a layer composed of the pressure-sensitive adhesive composition described above. The pressure-sensitive adhesive sheets include a so-called base material-less double faced pressure-sensitive adhesive sheet formed by firstly coating the layer of the above-described pressure-sensitive adhesive composition on a release liner so as to provide a dry thickness of usually about from 10 to 150 xcexcm and, if necessary, sticking a release liner to the surface of the layer. In this case, in order to improve the adhesive characteristics, a multilayer structure may be formed utilizing other pressure-sensitive adhesive compositions.
Also, as the more general pressure-sensitive adhesive sheet, a base material-attached single faced or double faced pressure-sensitive adhesive sheet can be formed by using a base material composed of a plastic film such as a polyester film, etc.; a porous material such as a paper, a non-woven fabric, etc.; a metal foil, etc., coating the layer composed of the above-described pressure-sensitive adhesive composition on one surface or both surfaces of the base material at a dry thickness of usually from about 10 to 150 xcexcm per one surface such that the base material carries the pressure-sensitive adhesive layer, and sticking a release liner on the surface(s) of the pressure-sensitive adhesive layer(s). In this case, to improve -the adhesive characteristics, a multilayer structure may be employed by utilizing other pressure-sensitive adhesive composition.
In addition, in the base material-attached pressure-sensitive adhesive sheets and the above-described base material-less double faced pressure-sensitive adhesive sheets, the crosslinking treatment to the polymer having the polycarbonate structure, etc., can be properly applied during the production step of the above-described pressure-sensitive adhesive sheets or after the production step.
In the present invention, as the release liner to be stuck to the pressure-sensitive adhesive layer surface, a release liner made up of a polyethylene film, a polypropylene film, etc., which is not subjected to a silicone release coating, can be used. That is, even when such a release liner is used, a very good releasing property such that the releasing strength of the liner is 200 g/50 mm width or lower, preferably 100 g/50 mm width or lower, and more preferably 50 g/50 mm width or lower (usually up to 1 g/50 mm width) can be obtained, and further the good adhesive strength described above can be maintained.
In conventional acrylic series or rubber series pressure-sensitive adhesives, when a polyethylene film or a polypropylene film is used as a release liner, the releasing strength is 500 g/50 mm width or higher to lower the releasing workability, whereby it is inevitable to use a silicone-treated release liner. In the present invention, using a release liner which is not subjected to a silicone release coating, the releasing strength thereof can be set to 200 g/50 mm width or lower, and the above-described liner can be easily removed and the pressure-sensitive adhesive sheets of the present invention can be handled in the same manner as the use of ordinary pressure-sensitive adhesive tapes having silicone-treated release liners. For this reason, the change of the apparatus, the working process, etc., accompanied by the change of the silicone-treated release liner to the above-described release liner is unnecessary.
As described above, in the pressure-sensitive adhesive sheets of the present invention, by using a polyethylene film, a polypropylene film, etc., as the release liner, the production of the pressure-sensitive adhesive sheets containing no silicone is possible and as the result thereof, the pressure-sensitive adhesive sheets suitable for computer instruments which are liable to cause a problem by the presence of a silicone can be provided. Furthermore, when the release liner is made up of a simple film material such as polyethylene or polypropylene, the effect of providing excellent recycling property of plastics, which is regarded as a problem remarkably in these days, can be obtained.
The release liner not subjected to a silicone release coating, which can be used in the present invention, includes polyolefin series films made up of polyethylene, polypropylene, an ethylene-propylene copolymer (block or random copolymer), or a mixture of them or films the surface of which is processed with the above-described polyolefins, that is, polyethylene, polypropylene, an ethylene-propylene copolymer (block or random copolymer) or a mixture of them. The film the surface of which is processed with the polyolefin described above includes, for example, a laminate of the above-described polyolefin series film and papers or other films.
In the present invention, as the pressure-sensitive adhesive sheet not using such a release liner, a pressure-sensitive adhesive sheet comprising a base material having formed on one surface thereof the layer being composed of the above-described pressure-sensitive adhesive composition and having the thickness described above and having at least the back side thereof constituted with a polyolefin such as polyethylene, polypropylene, an ethylene-propylene copolymer (block or random copolymer) or a mixture thereof can be also obtained.
The feature of the pressure-sensitive adhesive sheets of this kind is that the back side of the base material is not subjected to a silicone release coating, but the releasing property between the layer composed of the pressure-sensitive adhesive composition and the back surface of the base material is good, and thus, the pressure-sensitive adhesive sheet can be wound in a roll form without inserting a release liner. As described above, because the pressure-sensitive adhesive sheet does not have a release liner and it is unnecessary to apply a releasing coating with a silicone compound to the back surface of the base material, the pressure-sensitive adhesive sheet of the present invention can be advantageously used for computer instruments as a pressure-sensitive adhesive sheet substantially containing no silicone compound. In addition, if the anchoring property of the layer composed of the pressure-sensitive adhesive composition and the base material is ensured, not only the back side of the base material but also the whole base material may be constituted with the polyolefin described above.
Second, the present invention provides a sealing material comprising a sealing base material having formed thereon the layer of the pressure-sensitive adhesive composition, which is used as an adhesive seal for constituting parts in electron instruments particularly avoiding a siloxane gas, such as mainly a hard disc drive (hereinafter referred to as HDD), a personal computer, a word processor, personal digital assistance (portable information instrument for person; hereinafter referred to as PDA), a portable telephone, etc.
The constituting parts in HDD, a personal computer, a word processor, PDA, a portable telephone, etc., are various and as one of the connecting means of these parts, a method of using a pressure-sensitive adhesive-processed product such as a pressure-sensitive adhesive tape is known. In particular, in the housing constructing step of HDD, to secure the airtightness, a pressure-sensitive adhesive-processed sealing material, that is, a sealing material (packing material) prepared by forming a layer of a pressure-sensitive adhesive composition on a foamed base material or a base material having a moisture-proofing effect is used. For the pressure-sensitive adhesive composition of the sealing material of this kind, it is desired to show a high adhesive property and cohesive property, and recently, performance such as a low volatile property is also required.
Now, in such a pressure-sensitive adhesive-processed sealing material, a release liner is usually stuck to the surface of the pressure-sensitive adhesive layer to protect the surface of the pressure-sensitive adhesive layer and to improve the handling property at storage and at use. Also, as the case may be, the back surface of the sealing base material composed of a foamed base material or a base material having a moisture-proof effect is subjected to a releasing coating to improve the releasing property between the surface of the pressure-sensitive adhesive layer and the back surface of the base material, whereby the sealing material is wound in a roll form without inserting a release liner.
On the other hand, the conventional sealing materials are designed such that a good adhesive property is secured, i.e., almost all sealing materials have a release liner subjected to a silicone release coating which has a low adhesive property or the back surface is subjected to a silicone release coating to improve releasing property with the back surface thereof. This causes the following problem.
That is, in the sealing materials of this kind, a phenomenon that a part of a silicone compound existing in the release liner or at the back side of the sealing base material transfers to the surface of the layer of the pressure-sensitive adhesive composition occurs. The phenomenon is almost insignificant in the case of a usual sealing material, but in the case where the sealing material is used in the state of being closed in the inside of HDD, etc., it becomes the cause of generating a siloxane gas, which results in causing the corrosion of the inside of HDD and causing erroneous actions.
Under such circumstances, other object of the present invention is to provide a sealing material being excellent in the releasing property from a release liner or the back surface of the base material, showing a good adhesive strength, and having a high sealing effect by using a release liner which is not subjected to a silicone release coating and a sealing base material the back surface of which is not subjected to a silicone release coating.
As the result of various investigations, the present inventors have found that by providing the pressure-sensitive adhesive composition comprising the specific polymer having the polycarbonate structure on a sealing base material, a release liner (for example, composed of a polyethylene film) which is not subjected to a silicone release coating and a sealing base material having a back side (for example, one constituted with polyethylene) which is not subjected to a silicone release coating can be used, and a sealing material having excellent releasing property with the release liner or the back surface of the base material, showing a good adhesive property, and having a high sealing effect as the desired object can be obtained, and the problems of causing the corrosion of the inside, etc., of HDD and the erroneous actions by the generation of a siloxane gas are avoided by the sealing material, and have accomplished the present invention.
That is, according to still other aspect of the present invention, there is provided a sealing material comprising a sealing base material composed of a foamed base material or a base material having a moisture proof effect having thereon a layer composed of a pressure-sensitive adhesive composition comprising a polymer of a polycarbonate structure having a repeating unit represented by the following formula as described above; 
wherein R represents a straight chain or branched hydrocarbon group having from 2 to 20 carbon atoms.
In particular, the present invention provides a sealing base material wherein a release liner, which is not subjected to a silicone release coating, is stuck to the surface of the pressure-sensitive adhesive layer or the back side thereof is not subjected to a silicone release coating, and the sealing material is wound in a roll form without inserting a release liner and mainly provides the above-described sealing material as a connecting material for HDD, etc.
As the sealing base material to be used in this invention, known various materials can be used as long as the materials are provided with the sealing function as the desired purpose and do not substantially contain a silicone compound in the components of the materials. The typical sealing material is a sheet-form material or a foamed material of a synthetic resin or a synthetic rubber, such as polyurethane, a styrene-butadiene copolymer rubber (hereinafter referred to as SBR) or a material having an elastic effect made up of the laminate of these synthetic resin films. The thickness of the sealing material differs according to the form of the material, i.e., whether the material is a sheet-form material, a foamed material, or a laminate, but is generally from about 0.3 to 2.0 mm .
Another sealing material is a metal foil such as an aluminum foil, a fluorine resin film or a material having a moisture proof effect made up of a composite material obtained by forming a metal layer such as aluminum, etc., on a synthetic resin film such as a polyester film, etc., (laminating the metal foil or vapor depositing the metal on the synthetic resin film) or a composite material obtained by coating a fluorine resin layer on the synthetic resin film as described above. The thickness of the sealing material largely differs depending on whether the material is the metal foil, the fluorine resin film, or the laminate, but is preferably from about 10 to 200 xcexcm.
In addition, the fluorine resin constituting the fluorine resin film and the fluorine resin layer includes polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), a tetrafluoroethylene-hexafluoroporpylene copolymer (FEP), an ethylene-tetrafluoroethylene copolymer (E/TFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), an ethylene-chlorotrifluoroethylene copolymer (E/CTFE), a tetrafluoroethylene-perfluorodimethyldioxol copolymer (TEF/PDD), polyvinyl fluoride (PVF), etc.
The sealing material of the present invention is prepared by coating the layer composed of the above-described pressure-sensitive adhesive composition on the sealing base material as described above such that the layer has a dry thickness of usually from about 10 to 150 xcexcm. The layer of the pressure-sensitive adhesive composition may be formed on one surface of the base material but, if necessary, may be formed on both surfaces thereof. Also, for improving the adhesive characteristics, a multilayer structure may be employed using other pressure-sensitive adhesive composition.
In such a sealing material, a release liner, which is not subjected to a silicone release coating, is usually stuck to the surface of the pressure-sensitive adhesive surface, that is, the surface of the layer composed of the pressure-sensitive adhesive composition. The release liner includes a polyolefin series film made up of polyethylene, polypropylene, an ethylene-propylene copolymer (block or random copolymer) or a mixture thereof and a film processed with the foregoing polyolefin, i.e., polyethylene, polypropylene, an ethylene-propylene copolymer (block or random copolymer) or a mixture thereof and the latter film the surface of which is processed also includes a laminate of the above-described polyolefin series film and papers or other films. The thickness of the release liner which is not subjected to a silicone release coating is usually from about 20 to 200 xcexcm.
The sealing material of the present invention thus constituted is excellent in the releasing property and shows a large adhesive strength such that the releasing strength of the release liner is 200 g/50 mm width or lower, preferably 100 g/50 mm width or lower, and more preferably 50 g/50 mm width or lower (usually up to 1 g/50 mm width) and the adhesive strength is 1 kg/20 mm width or higher and preferably 1.5 kg/20 mm width or higher (usually up to 10 kg/20 mm width).
As described above, the sealing material of the present invention contains no silicone by utilizing a polyethylene film, a polypropylene film, etc., as the release liner and thus is particularly useful as a connecting material for HDD, etc., causing a problem by the generation of a siloxane gas. Also, when the release liner is made up of a simple film material such as polyethylene, polypropylene, etc., the sealing material is also excellent in the recycling property of plastics, which is particularly regarded as a problem recently.
Also, when in general acrylic or rubber series pressure-sensitive adhesives, a polyethylene film, a polypropylene film, etc., is used as the release liner, the releasing strength becomes 500 g/50 mm width or higher, whereby the problem of lowering the releasing workability cannot be avoided. In the present invention, such a problem does not occur. That is, because the releasing strength of the release liner can be set to 200 g/50 mm width or lower in the sealing material of the present invention, the release liner can be easily removed from the sealing material and the sealing material of this invention can be handled as the case of an ordinary sealing material having a silicone-treated release liner. As a result thereof, the advantage is obtained that the change of the apparatus, the working process, etc., accompanied by the change of the silicone-treated release liner to the above-described release liner of the present invention, which is not subjected to a silicone release coating, is unnecessary.
In the present invention, as a so-called liner-less sealing material not using such a release liner, a sealing material can be obtained by forming the layer of the above-described pressure-sensitive adhesive composition on one side of a sealing base material and winding in a roll form without applying a silicone release coating to the back side of the sealing base material and without inserting a release liner. In particular, the back side of a sealing base material is constituted with a polyolefin such as polyethylene, polypropylene, an ethylene-propylene copolymer, or a mixture thereof, and the sealing material can be wound in a roll form without inserting a release liner to obtain a roll-form wound sealing material.
Though the sealing material does not have a release liner and the back side of the sealing base material is not subjected to a silicone release coating, the material has a moderate releasing property with the back surface of the base material and a releasing strength adjusted to the same value as the case of using the aforesaid release liner, and also can maintain the adhesive strength as the case described above. Accordingly, the sealing material of this invention can be used as a connecting material for HDD, etc., which is the same use as the case of using the above-described release liner not subjected to a silicone release coating, as a sealing material substantially containing no silicone compound.
The 3rd aspect of the present invention provides a reinforcing sheet comprising an insulating base material and an adhesive layer which is used for reinforcing the terminal portions of a tape electric wire.
Recently, with the propagation of OA equipments and the development of LAN, multicore cables called xe2x80x9ctape electric wiresxe2x80x9d (or xe2x80x9cflat cablesxe2x80x9d) have been widely used. The tape electric wire of this kind has a structure that a definite number (not less than 2) of electrically conductive wires are disposed in an insulating layer in parallel to each other at an interval.
In the case of connecting the terminal of the tape electric wire, the insulating layer is removed at the terminal to expose the electrically conductive wires, and a reinforcing sheet is adhered to the exposed portions. As the reinforcing sheet, the sheets described, for example, in JU-A-61-93936 (the term xe2x80x9cJU-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese utility model applicationxe2x80x9d), JP-A-3-283312, JP-4-298980, JP-A-6-260249, and JP-A-6-260250 are known.
The reinforcing sheet has a structure that an adhesive layer, which is to be adhered to the insulating layer (polyester film) and the electrically conductive wires of the terminal portion of the tape electric wire, is formed on one surface of the insulating base material which becomes a reinforcing layer. Also, the adhesive layer is a structure of stripe coating, double coating, etc., by selecting an adhesive suitable for each adherend for strongly adhering to each of the insulating layer and the electrically conductive wires.
Furthermore, as the components for the adhesive, a thermoplastic copolymerized polyester resin, an epoxy group-containing ethylene copolymer, a vinyl aromatic hydrocarbon polymer, an acrylic acid ester series polymer, a rubbery material, an ethylenic polymer, etc., are recommended. However, in almost all cases, considering the balance characteristics of the adhesive property to the insulating layer (polyester film) and the electrically conductive wires of the tape electric wires, the adhesive property with the insulating base material (reinforcing layer), etc., the thermoplastic copolymerized polyester resin has been widely used.
However, in conventional reinforcing sheets using the thermoplastic copolymerized polyester resin as the adhesive layer, in almost all cases, the adhesive strength at a normal temperature atmosphere (10 to 50xc2x0 C.) is insufficient or even when the adhesive strength at a normal temperature atmosphere is good, the adhesive strength at a low-temperature atmosphere (lower than 10xc2x0 C., particularly lower than 0xc2x0 C.) or at a high-temperature atmosphere (higher than 50xc2x0 C. and not higher than 80xc2x0 C.) is insufficient.
The present invention has been made under these circumstances and the object of the present invention is to provide a reinforcing sheet comprising an insulating base material and an adhesive layer for reinforcing the terminal portion of a tape electric wire, which is excellent in the adhesive property to the tape electric wires even under a low-temperature atmosphere.
As the result of various investigations of material construction of the adhesive layer formed on one surface of an insulating base material for attaining the above-described object, the present inventors have found that by using the above-described specific polyester as the base polymer and properly crosslinking the base polymer, a reinforcing sheet having a very excellent adhesive property with tape electric wires under the environment from normal temperature to a low temperate can be obtained and have accomplished the present invention.
That is, the present invention provides a reinforcing sheet for reinforcing the terminal portion of a tape electric wire having such a structure that electrically conductive wires are disposed in an insulating layer at an interval, comprising an insulating base material having formed on one surface thereof a pressure-sensitive adhesive layer comprising the above-described specific polyester, and in particular, the above-described reinforcing sheet wherein the above-described polyester is further subjected to a crosslinking treatment and the solvent-insoluble component of the pressure-sensitive adhesive layer is at least 15% by weight can be provided.
In the reinforcing sheet of the present invention, as the insulating base material, any material may be used as long as the material effectively functions as a reinforcing layer for the terminal portion of a tape electric wire and, for example, a plastic film such as a polyester film, etc., having a thickness of usually from about 50 to 350 xcexcm or a porous material such as a paper, a non-woven fabric, etc., is used.
In the reinforcing sheet of the present invention, the thickness of the pressure-sensitive adhesive layer formed on one surface of the above-described insulating base material is usually from about 10 to 150 xcexcm and as a pressure-sensitive adhesive composition showing a good adhesive property to the above-described base material and also to the insulating layer and the conductive wires constituting the tape electric wire, and in particular, showing a good adhesive strength under a low-temperature environment of not higher than about 0xc2x0 C., the pressure-sensitive adhesive composition prepared using the above-described specific polyester as the base polymer is used.
The components constituting the specific polyester, the method of crosslinking the polyester, the crosslinking agent, etc., are the same as described above, and the used amount of the above-described polyfunctional compound as the crosslinking agent is properly selected according to the balance with the polyester to be crosslinked. In general, it is better to carry out the crosslinking treatment by combining the crosslinking agent in an amount of at least about 0.5 part by weight, and preferably from about 1 to 4 parts by weight per 100 parts by weight of the polyester, whereby the pressure-sensitive adhesive composition, in which the solvent-insoluble component is 15% by weight or more, and preferably 20% by weight or more (usually up to 70% by weight), can be obtained. If the solvent-insoluble component of the pressure-sensitive adhesive component is less than 15% by weight, the cohesive force is insufficient and a sufficient adhesive property can not be obtained.
The used amount of the above-described polyfunctional compound is properly selected according to the balance with the polyester to be crosslinked. In general, it is better to carry out the crosslinking treatment by compounding the polyfunctional compound in an amount of at least about 0.5 part by weight, and preferably from about 1 to 4 parts by weight per 100 parts by weight of the polyester, whereby the pressure-sensitive adhesive composition wherein the solvent-insoluble component is 15% by weight or more, and preferably 20% by weight or more (usually up to 70% by weight) can be obtained. If the solvent-insoluble component of the pressure-sensitive adhesive composition is less than 15% by weight, the cohesive force is insufficient and a sufficient adhesive property can not be obtained.
As other crosslinking means, there is a method of compounding the above-described polyfunctional monomer as a crosslinking agent with the polyester and crosslinking the polyester by electron rays, etc. It is better that the used amount of the polyfunctional monomer is at least about 1 part by weight, and preferably from about 2 to 4 parts by weight per 100 parts by weight of the polyester such that the solvent-insoluble component of the pressure-sensitive adhesive composition after crosslinked by electron rays falls within the above-described values.
In the reinforcing sheet of the present invention, the thickness of the pressure-sensitive adhesive layer formed on one surface of the above-described insulating base material is usually from about 10 to 150 xcexcm, and as the pressure-sensitive adhesive composition showing a good adhesive property to the above-described base material and the insulating layer and the conductive wires constituting the tape electric wire and, in particular, showing a good adhesive property in the atmosphere from a low temperature atmosphere of lower than 10xc2x0 C. to a normal temperature atmosphere of from 10 to 50xc2x0 C. and in a high-temperature atmosphere of from higher than 50 to 80xc2x0 C., the following specific pressure-sensitive adhesive composition is used.
The specific pressure-sensitive adhesive composition is preferably the composition comprising, along with the above-described polymer having the polycarbonate structure, a resin having a softening point of at least 80xc2x0 C. in a ratio of from 10 to 50% by weight of the sum total of the polymer and the resin. The content of the resin is from 10 to 50% by weight, preferably from 13 to 45% by weight, and more preferably from 15 to 35% by weight. If the content of the resin is more than 50% by weight, the shock resistance at a low temperature is lowered and if the content is less than 10% by weight, the shear adhesive strength is lowered, and in both cases, it becomes difficult to show a good adhesive strength in a wide temperature range of from a low temperature to a high temperature.
It is better that the pressure-sensitive adhesive composition used in this case contains the polymer having the polycarbonate structure and the specific resin in the above-described ratios and the content of the solvent-insoluble component is set in the range of preferably from 10 to 90% by weight, more preferably from 15 to 85% by weight, and still more preferably from 20 to 80% by weight. If the content of the solvent insoluble component is too low, the durability is inferior and if the content is too high, the adhesive property is inferior. Thus, both cases are not preferred.
The pressure-sensitive adhesive composition may further contain additives usually used, for example, a crosslinking agent such as an epoxy compound, an isocyanate compound, etc.; a filler such as glass fibers, a metal powder, etc., a pigment, a coloring agent, and a plasticizer.
Reinforcing the terminal portion of a tape electric wire by the use of the reinforcing sheet of the present invention thus constituted can be carried out according to an ordinary method. For example, after removing an insulating layer at the terminal portion of a tape electric wire having a structure such that 2 or more electrically conductive wires are disposed in an insulating layer at an interval to thereby expose the conductive wires, the above-described reinforcing sheet of the present invention is adhered to the exposed portion by utilizing adhesive strength of the pressure-sensitive adhesive layer to reinforce the foregoing terminal portion.
The 4th aspect of the present invention is a printable pressure-sensitive adhesive sheet.
That is, because a silicone thin film which prevents attaching of a viscous material is not formed on the back surface of the base material of the above-described pressure-sensitive adhesive sheet, by using an ink ribbon coated with an ink containing a plastic component (e.g., the resin same as or similar to the base material) having an adhesive property to the base material and a coloring agent (e.g. organic or inorganic, dyes or pigments), heat-transferring the ink of the ink ribbon onto the back surface of the base material by a heat-transfer printer generally known, the ink is adhered to the back surface by a physical means such as welding, melt-attaching, etc., whereby printing can be applied.
Accordingly, in such a printing use, the base material is preferably porous in the point of the close attaching property, and also when the base material has a hiding property, the print can be clearly recognized in the relation with contrast.
There is no particular restriction on the means of making porous and, for example, the porous base material can be obtained by imparting strain to the base material and also forming fine cracks by a stretching operation. Such a stretching operation simultaneously imparts a light scattering function to the base material, and the hiding property is therefore improved.
The hiding property can be also obtained by compounding a filler, etc., but the porous base material may be composed of plural layers such that the back side is constituted with a polyolefin layer and a layer between the polyolefin layer and a pressure-sensitive adhesive layer is constituted with an opaque material (e.g., a paper) as a support layer.